1. Field of the Invention
The present invention relates to a bearing, and more specifically, to an oil impregnated sintered bearing which is suitable for use as a bearing of a motor without side pressure such as a spindle motor.
2. Background Prior Art
A spindle motor is used as a rotation and drive source in a compact disk player, a video disk player, a floppy disk drive device and the like. Such spindle motor merely rotates and receives no side pressure. In the case where a slide bearing is used for such a motor as described, a vibration occurs during rotation due to play between the motor shaft and the bearing.
In view of the above, the following measures have been heretofore taken for the bearing of a motor which receives no side pressure such as a spindle motor in order to minimize the vibration of the shaft:
1. Clearance between the bearing and the shaft is reduced by about 15 .mu.m to 2-3 .mu.m of normal clearance;
2. A magnet or the like, for example, is mounted on a stator to attract a rotor in order to apply a side pressure load;
3. A dynamic pressure bearing such as a groove bearing is used.
In the above described method (1), however, the vibration becomes small but a non-periodic vibration occurs. It is also very difficult, in terms of precision, to machine parts with accuracy of 2 to 3 .mu.m.
In the construction mentioned in (2) above, such construction for applying side pressure becomes complicated.
In the case of the method (3), such approach is effective for reducing vibrations. However, since a groove is normally formed by etching, such bearing is expensive when compared with ordinary bearings. Moreover, this approach involves a supply of oil and a seal in its construction. When oil supply is short, a dynamic pressure effect cannot be obtained, resulting in occurrence of burn. In addition, since the groove for obtaining the dynamic pressure effect is a special one, an extremely precise machining technique is required.